title: Enhanced Ig production by human peripheral lymphocytes induced by aggregated C1q.
abstract: Because B cells express receptors for C1q, we have investigated the role of C1q in the stimulation of B cells. When B cells were cultured in the presence of C1q that had been frozen, T cells, and suboptimal concentrations of PWM, there was a dose-dependent enhancement of IgM, IgG, and IgA by the B cells. No significant enhancement of Ig production by B cells was seen in the absence of T cells or PWM. The contribution of T cells or PWM could be replaced by supernatants of PMA and Con A-activated PBMC (T cell growth factor). C1q that had been frozen, in contrast with freshly isolated C1q, was at least 3 times more active in enhancement of the production of Ig by B cells in culture in the presence of suboptimal concentrations of T cell growth factor. The capability of C1q to stimulate B cells could be ascribed to aggregates of C1q. Monomeric C1q was only marginally active to stimulate B cell Ig production, whereas dimeric and tetrameric C1q were able to enhance Ig production by B cells in relation to their size. Furthermore, aggregation of C1q on soluble aggregates of rabbit IgM also increased its potential to enhance B cell Ig production. The interaction of C1q with the B cells occurs via the collagenous tail of C1q, as suggested by inhibition experiments with purified collagenous tails and globular heads of C1q. These results indicate that triggering of C1qR on B cells positively regulates Ig production in vitro.
authors.affiliation: Department of Nephrology, University Hospital Leiden, The Netherlands.
authors.forename: M R
authors.initials: MR
authors.lastname: Daha
authors.forename: N
authors.initials: N
authors.lastname: Klar
authors.forename: R
authors.initials: R
authors.lastname: Hoekzema
authors.forename: L A
authors.initials: LA
authors.lastname: van Es
mesh_terms: D000917:Antibody Formation; D001402:B-Lymphocytes / Q000276:immunology*; D002478:Cells, Cultured; D015922:Complement C1q / Q000276:immunology / Q000494:pharmacology*; D004306:Dose-Response Relationship, Immunologic; D006801:Humans; D066298:In Vitro Techniques; D007376:Interleukin-2 / Q000494:pharmacology; D009000:Monocytes / Q000502:physiology; D011043:Pokeweed Mitogens / Q000494:pharmacology; D013329:Structure-Activity Relationship
chemical_list: D007376:Interleukin-2; D011043:Pokeweed Mitogens; D015922:Complement C1q